1. Field of the Invention
The present invention relates to a fixing roller of an image forming apparatus.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus scans an image carrying medium with a laser beam projected by a laser scan unit, thereby producing an electrostatic latent image on a surface of the image carrying medium. Developer, such as toner, is provided to the electrostatic latent image by a developing device and a toner image is visualized.
The visible image is transferred onto a printing paper that passes through the image carrying medium and a transferring roller. As the printing paper passes through a space between a fixing roller and a backup roller rotating in contact with each other, the visible image is fixed onto the printing paper by heat and pressure.
Recently, fixing rollers have adopted an inductive heating system. In the fixing roller applying the inductive heating system, an induction coil is disposed within a passive heating roller comprising a magnetic substance, and an insulator layer is provided between the induction coil and the passive heating roller. Because the passive heating roller is a rotatable part in this structure, the induction coil is preferably contacted as tightly as possible with the passive heating roller to enhance inductive heating efficiency by interlinking magnetism generated from the induction coil and the passive heating roller.
In a conventional structure, an extension coil spring is interposed within the passive heating roller, thereby tightly contacting the induction coil with an inside of the passive heating roller, so that the induction coil is rotated as tightly contacted with the passive heating roller by a pressure applied toward an inside of the coil spring. The insulator is interposed between the induction coil and the coil spring.
However, as a printing speed of a printer increases, a rotational speed of the fixing roller increases accordingly. When the rotational speed of the fixing roller increases, slip of the coil spring or idle rotation of the fixing roller may be caused. As a result, the induction coil may be disconnected or twisted.
Accordingly, a need exists for an image forming apparatus having an improved fixing roller having an inducting coil tightly disposed therein that is substantially prevented from slipping or idle rotation with respect to an inner surface of the roller body.